1. Osteoarthritis
Osteoarthritis (OA) is a chronic joint disease characterized by progressive degeneration of articular cartilage. Symptoms include joint pain and impaired movement. OA is one of the leading causes of disability worldwide and a major financial burden to health care systems. It is estimated to affect over 15 million adults in the United States alone. See Boh L. E. Osteoarthritis. In: DiPiro J. T., Talbert R. L., Yee G. C., et al., editors. Pharmacotherapy: a pathophysiological approach. 4th ed. Norwalk (Conn.): Appleton & Lange, pp. 1441-59 (1999).
Oral non-steroidal anti-inflammatory drugs (NSAIDs) are a mainstay in the management of OA. They have analgesic, anti-inflammatory and antipyretic effects and are useful in reducing pain and inflammation. NSAIDS are however associated with serious potential side effects including nausea, vomiting, peptic ulcer disease, GI haemorrhage, and cardiovascular events.
Topical NSAIDs offer the possibility of achieving local therapeutic benefit while reducing or eliminating the risk of systemic side effects. There has been widespread interest in this approach to treating OA, but data in support of the efficacy of topical NSAIDs in the treatment of OA is limited. For instance, a study of 13 randomized placebo controlled trials (RCT's) of various topical NSAIDs tested specifically for use in the treatment of OA concluded that they were not generally efficacious for chronic use in OA. (Lin et al., Efficacy of topical non-steroidal anti-inflammatory drugs in the treatment of osteoarthritis: meta-analysis of randomized controlled trials, BMJ, doi:10.1136/bmj.38159.639028.7C (2004)).
There are generally three outcomes used to measure the efficacy of an OA treatment: pain, physical function, and a patient global assessment. See Bellamy N., Kirwan J., Boers M., Brooks P., Strand V., Tugwell P., et al. Recommendations for a core set of outcome measures for future phase III clinical trials in knee, hip and hand osteoarthritis. Consensus development at OMERACT III., J. Rheumatol, 24:799-802 (1997). To be suitable for chronic use, a therapy must generally show efficacy on these three variables over a sustained period of time. In the U.S. for instance, the Food and Drug Administration (FDA) requires OA therapies to show superiority over placebo over a 12 week period. Notwithstanding the significant potential for topical NSAIDs in the treatment of OA, as of the time of filing this application, none have been approved for such treatment in the U.S.
U.S. Pat. Nos. 4,575,515 and 4,652,557 disclose topical NSAID compositions, one of which, consisting of 1.5% diclofenac sodium, 45.5% dimethylsulphoxide, 11.79% ethanol, 11.2% propylene glycol, 11.2% glycerine, and water, has been shown to be effective in chronic OA treatment. See Towheed, Journal of Rheumatology 33:3 567-573 (2006) and also Oregon Evidence Based Practice Center entitled “Comparative Safety and Effectiveness of Analgesics for Osteoarthritis”, AHRQ Pub. No. 06-EHC009-EF. This particular composition is referred to herein as “comparative liquid formulation” or “comparative” in the Examples section. However, the compositions of these prior inventions have drawbacks in that they are slow to dry and runny. They also require frequent dosing of three to four times a day to achieve efficacy in OA, which increases exposure to potential skin irritants and increases the risk of skin irritation.
In general, the failure of topical NSAIDs to fulfill their promise in OA may be due in part to the difficulty associated with delivering a molecule through the skin in sufficient quantities to exert a therapeutic effect and in a manner that makes the treatment itself tolerable. It is generally believed that clinical efficacy in OA requires absorption of the active ingredient and its penetration in sufficient quantities into underlying inflamed tissues including the synovium and synovial fluid of joints. See Rosenstein, Topical agents in the treatment of rheumatic disorders, Rheum. Dis. Clin North Am., 25: 899-918 (1999).
However, the skin is a significant barrier to drug permeation, and despite nearly four decades of extensive research, the success of transdermal drug delivery in general remains fairly limited with only a small number of transdermal drug products commercially available.
In connection with topical dosage forms applied to the skin, a number of interactions can occur including vehicle-skin, vehicle-drug, and drug-skin. Each can affect the release of an active agent from a topical dosage form (Roberts, M. S.: Structure-permeability considerations in percutaneous absorption. In Prediction of Percutaneous Penetration, ed. by R. C. Scott et al., vol. 2, pp. 210-228, IBC Technical Services, London, 1991). Thus various factors can affect absorption rates and penetration depth including the active ingredient, the vehicle, the pH, and the relative solubility of the active in the vehicle versus the skin (Ostrenga J. et al., Significance of vehicle composition I: relationship between topical vehicle composition, skin penetrability, and clinical efficacy, Journal of Pharmaceutical Sciences, 60: 1175-1179 (1971)). More specifically, drug attributes such as solubility, size and charge, as well as, vehicle attributes such as the drug dissolution rate, spreading-ability, adhesion, and ability to alter membrane permeability can have significant effects on permeability.
There is significant variability observed from seemingly minor variations in formulations. For instance, Naito demonstrates significant variability in penetration among topical NSAID formulations simply by changing the gelling agent used in the compositions (Naito et al., Percutaneous absorption of diclofenac sodium ointment, Int. Jour. of Pharmaceutics, 24: 115-124 (1985)). Similarly, Ho noted significant variability in penetration by changing the proportions of alcohol, propylene glycol, and water (Ho et al., The influence of cosolvents on the in-vitro percutaneous penetration of diclofenac sodium from a gel system, J. Pharm. Pharmacol., 46:636-642 (1994)). It was noted that the changes affected three distinct variables: (i) the solubility of the drug in the vehicle, (ii) the partition coefficient, and (iii) effects on alteration of skin structure.
Ho et al. (1994) also noted that (i) the pH of the vehicle, (ii) the drug solubility, and (iii) the viscosity of a gel matrix can influence penetration from a gel dosage form. The pH value affects the balance between ionized and non-ionized forms of the drug, which have different penetration properties (Obata, International Journal of Pharmaceutics, 89: 191-198 (1993)). The viscosity can affect diffusion of the drug through the gel matrix and release of the drug from the vehicle into the skin. The solubility of the drug in the vehicle will affect the partition coefficient of the drug between the formulation and the recipient membrane/tissue (Ho et al. 1994).
Chemical penetration enhancers are one means for reversibly lowering the skin barrier. Other methods include iontophoresis, ultrasound, electroporation, heat, and microneedles. At least 250 chemicals have been identified as enhancers that can increase skin permeability. General categories include pyrrolidones, fatty acids, esters and alcohols, sulfoxides, essential oils, terpenes, oxazoldines, surfactants, polyols, azone and derivatives, and epidermal enzymes.
The mechanisms by which penetration enhancers reduce the skin barrier function are not well understood (see Williams and Barry “Penetration Enhancers” Advanced Drug Delivery Reviews 56: 603-618 (2004)) although it has been proposed that the mechanisms can be grouped into three broad categories: lipid disruption, increasing corneocyte permeability, and promoting partitioning of the drug into the tissue.
The challenge with use of chemical penetration enhancers is that few seem to induce a significant or therapeutic enhancement of drug transport at tolerable levels. This is because the act of disrupting the skin barrier will have the potential of causing skin irritation. With increased disruption, skin irritation will become a greater issue. This is particularly problematic with topical OA treatments where the goal is to have the active penetrate into joint tissue and where the drug must be utilized on a long-term basis due to the nature of the disease. The inventors have developed methods and compositions that deliver more active ingredient per unit dose than previously known compositions, and this would be expected to lead to a lower incidence of skin irritation.
The compositions of the invention use diclofenac sodium which is a commonly used NSAID. Diclofenac has four different salts that show significant variability in the degree of permeation in solutions using different solvents. Minghetti, for instance, teaches that a diclofenac salt with an organic base is best for topical applications (Minghetti et al., Ex vivo study of trandermal permeation of four diclofenac salts from different vehicles, Jour. of Pharm. Sci, DOI 10.1002/jps.20770 (2007)).
Other research points to microemulsion formulations as a means for delivery of diclofenac sodium (Kantarci et al., In vitro permeation of diclofenac sodium from novel microemulsion formulations through rabbit skin, Drug Development Research, 65:17-25 (2005); and Sarigullu I. et al., Transdermal delivery of diclofenac sodium through rat skin from various formulations, APS PharmSciTech, 7(4) Article 88, E1-E7 (2006)).
Other topical diclofenac compositions are disclosed in a number of patents including U.S. Pat. Nos. 4,543,251, 4,670,254, 5,374,661, 5,738,869, 6,399,093 and 6,004,566. United States Patent Application No. 20050158348 points out that various solvents are widely used for gel preparations, but notes that they are limited in potential due to skin irritation. This reference also notes that gel compositions are associated with fast termination of action as the active precipitates from solution in the upper skin layers, limiting anti-inflammatory action in deeper tissues. The gels of the present invention are designed to accomplish the opposite, namely prolonged action and anti-inflammatory action in the deeper tissues.
2. Gel Formulations of Diclofenac
None of the previous references disclose the compositions of the invention or their use in the treatment of OA. Rather, these references highlight the significant unmet need with respect to topical OA treatments for chronic use and the complexity of transdermal transport in general, where significant variability in permeation is observed by changing composition elements or their relative proportions.
In light of the foregoing, there is a considerable need for improvement in the development of a topical NSAID suitable for long term use in the treatment of OA. The challenge has been to develop an optimal formulation which will deliver the active agent to the underlying tissue in sufficient concentration to treat OA on a long term basis, while reducing or minimizing the incidence of intolerable skin irritation caused by disrupting the skin barrier and while providing a formulation and dosage that leads to and encourages patient compliance. The present invention satisfies these and other needs.